Former NFL safety Sergio Brown is fighting back in his murder case this week ... pleading not guilty to charges that he killed his mom and concealed her body afterward.
According to a spokesperson for the Cook County State's Attorney's Office, Brown entered the pleas before an Illinois judge on Wednesday.
He's now due back for another hearing in the case late next month.
As we previously reported, Brown was first hit with one charge of first-degree murder and one count of concealment of a dead body back in October .